The present invention is generally directed to an implantable device for monitoring the progression or regression of heart disease. The present invention is more particularly directed to a system and method for use in an implantable cardiac stimulation device which determines and stores interchamber conduction delays. Relative changes in the interchamber conduction delays, over time, are indicative of the progression or regression of the heart disease.
More people die of heart disease than any other single cause. One common form of heart disease is congestive heart failure.
Congestive heart failure (CHF) is a debilitating, disease in which abnormal function of the heart leads to inadequate blood flow to fulfill the needs of the body""s tissues. Typically, the heart loses propulsive power because the cardiac muscle loses capacity to stretch and contract. Often, the ventricles do not adequately fill with blood between heartbeats and the valves regulating blood flow may become leaky, allowing regurgitation or backflow of blood. The impairment of arterial circulation deprives vital organs of oxygen and nutrients. Fatigue, weakness, and inability to carry out daily tasks may result.
Not all CHF patients suffer debilitating symptoms immediately. Some may live actively for years. Yet, with few exceptions, the disease is relentlessly progressive.
As CHF progresses, it tends to become increasingly difficult to manage. Even the compensatory responses it triggers in the body may themselves eventually complicate the clinical prognosis. For example, when the heart attempts to compensate for reduced cardiac output, it adds sarcomeres to the myocardial cells, causing the ventricles to grow in mass in an attempt to pump more blood with each heartbeat. This places a still higher demand on the heart""s oxygen supply. If the oxygen supply falls short of the growing demand, as it often does, further injury to the heart may result. The additional muscle mass may also stiffen the heart walls to hamper rather than assist in providing cardiac output.
Current standard treatment for heart failure is typically centered around medical treatment using ACE inhibitors, diuretics, and digitalis. It has also been demonstrated that aerobic exercise may improve exercise tolerance, improve quality of life, and decrease symptoms. Heart transplantation is an option, but only in 1 out of 200 cases. Other cardiac surgery may also be indicated, but only for a small percentage of patients with particular etiologies. Although advances in pharmacological therapy have significantly improved the survival rate and quality of life of patients, patients who are refractory to drug therapy have a poor prognosis and limited exercise tolerance. Cardiac pacing has been proposed as a new treatment for patients with drug-refractory CHF.
In patients with heart failure and atrial fibrillation (AF), the heart has often remodeled due to the disease, such that there is increased fibrosis between myocardial cells, a lengthening of the cells, varying degrees of hypertrophy and dilation, and up and down regulation of various receptors that affect ionic balance, action potential conduction, and contraction. These variations in the AF and CHF substrates often result in conduction abnormalities that may manifest in arrhythmia, which may further worsen the substrate and thus the heart""s contraction synchrony.
Multi-chamber pacing (bi-ventricular or bi-atrial) has been proposed as an emerging therapy for the treatment of heart failure and atrial fibrillation. The patients who appear to gain the greatest benefit from this pacing therapy are those with the greatest dyssynchrony, since the benefit of multi-chamber pacing appears dependent upon chamber synchronization and/or appropriate sequencing.
It is desirable to have a system which would track the progression or regression of the patient""s disease, particularly as it relates to the success of any therapy in halting or reversing the remodeling. A good metric of the heart""s reverse remodeling is the degree to which the myocardium conducts the depolarization wave, since this relates directly to chamber synchrony.
The hemodynamic consequences of abnormal ventricular activation in dilated cardiomyopathy patients have been extensively studied. These studies account for the presence of major delay and nonuniformity in left ventricular (LV) contraction and relaxation in patients with poor LV function and high-degree interventricular conduction block. Hence, the degree of interventricular conduction delay may be used as a surrogate measurement for the disease state of heart. Additionally, patients prone to atrial fibrillation are likely to have a long interatrial conduction delay. Restoration of atrial chamber synchrony/sequencing may be critical in reducing the incidence of AF in these patients.
By tracking the progression or regression of heart disease, such as CHF, more closely, treatments could be managed more effectively. Commonly, patients with heart disease have an implanted cardiac stimulation device. Hence, it would be advantageous if the implanted cardiac stimulation device were able to aid in the tracking of the progression or regression of the heart disease. The present invention provides a system and method for use in such a device capable of tracking heart disease progression or regression by measuring interchamber conduction delays over time.
The present invention provides a system and method, for use in an implantable cardiac stimulation device, for monitoring progression or regression in heart disease such as congestive heart failure. A sensing circuit produces an electrogram signal indicative of the electrical activity of the patient""s heart. A processor processes the electrogram signal to determine interchamber conduction delays which are then stored in memory. The stored interchamber conduction delays may be retrieved by way of a telemetry circuit. Relative changes in the interchamber conduction delays, over time, are indicative of progression or regression in the heart disease.
The determined interchamber conduction delays may be the times between activations of corresponding ventricular or atrial chambers of the heart. The interchamber delays may alternatively be the times between the delivery of a pacing pulse to one chamber and the intrinsic depolarization of its corresponding chamber. The interchamber conduction delays may alternatively be the average of the right chamber to left chamber conduction delay and the left chamber to right chamber conduction delay.
The relative changes in the interchamber conduction delays may be further used for automatic pacing parameter adjustment. If the relative changes in the interchamber conduction delays indicate a decreasing trend, pacing rate may be decreased or AV delay may be increased to allow the patient""s heart to function more on its own without pacing intervention.